This disclosure relates in general to measuring properties of a multiphase mixture flowing in a pipe and, more specifically, but not by way of limitation, to using probes with different sensitivity depths to measure a liquid fraction and a water liquid ratio for a liquid phase of the multiphase mixture.
In the hydrocarbon industry, surface monitoring of oil and gas producing wells is tending towards metering multiphase flows with a wide range of gas volume flow fraction (“GVF”). An example of this are so called wet-gas-wells, where the GVF is typically larger than 95% and the liquid flow rate is typically no more than a few hundred barrels per day. For such production wells, it is often required to measure the gas flow rate and the liquid flow rate, as well as the composition of the liquid phase, e.g. water/liquid hydrocarbon ratio. For wells with GVF<95%, in-line multiphase flow meters may be used to measure flow properties. However, at GVFs above 95%, in-line metering may be problematic and the existing approaches for metering high GVF flows are separation and mixing. The separation approach provides for splitting the flow to be measured/characterized into an almost liquid flow plus an almost gas flow and then separately metering the separated flows using single-phase flow meters. The mixing approach attempts to minimize the slip between the different phases so that the velocity and holdup measurements may be obtained.
The existing methods are largely capable of providing good accuracy for metering gas flows with high GVF, however, the measurements of the liquid flow properties may be inaccurate. The disadvantages of the existing metering methods include increased cost associated with the separation and mixing devices and pressure drop in the pipeline and/or disruption to the flow in the pipeline resulting from the introduction of the separation and/or mixing devices into the pipeline carrying the hydrocarbon mixtures. Additionally, at high GVF, the mixing method may not provide for accurately measuring the holdup and water-in-liquid ratio (“WLR”) because the liquid holdup is very low under such conditions.